Airwasher systems, predominantly found in textile, electronics, pharmaceutical, and tobacco industries, provide humidity and temperature control in such plants. During the winter, airwasher systems increase the humidity in circulated air and during the summer, airwasher systems dehumidify recycled air. The removal of dust, odors, and particulates from the circulated air is another important function of air filtration and airwasher systems.
The most common design of an airwasher system is the vertical airwasher. Another system design still being used is the horizontal airwasher. Regardless of the design, airwasher systems have common features such as the basin, spray header trees and nozzles, and eliminator blades.
While a variety of problems can occur in the operation of airwasher systems, the most serious are poor corrosion control, where corrosion products can clog the spray headers, resulting in decreased airwasher efficiency. Other factors that can lead to spray nozzle plugging, specifically in the textile industry, include contaminants such as lint, cotton fibers and sizing agents such as polyvinyl alcohol, starches, waxes, and the like. An additional problem in such systems is the fouling of the equipment caused by microbiological activity.
Water soluble polymers such as polyacrylic acid have been utilized as additives to disperse solids contained in industrial cooling water systems and as an aid to prevent the adherence of scale on the metallic surfaces of such systems in contact with water. Likewise, biocides have been added to control the formation of microbiological growth in industrial systems. The presence of microbiological growth can provide a location where corrosion can occur, underneath the deposit and where water flow is minimal and untreated.
However, due to the pending environmental regulations and restrictions, a non-metal, non-phosphorus corrosion inhibiting program is needed for use in the industries that typically employ airwasher systems.
Shim et al., U.S. Pat. No. 5,589,106 discloses compositions for preventing corrosion of metallic surfaces in contact with industrial cooling water comprising: a hydrocarboxylic acid or its water soluble salts, a water-soluble alkali metal silicate, a water-soluble dispersant polymer, and optionally other corrosion inhibitors and biocides. Persinski et al., U.S. Pat. No. 4,640,793 discloses synergistic compositions which act as scale and corrosion inhibitors comprising two water-soluble polymers.
Neither Shim et al. nor Persinski et al. describes a composition for the treatment of air washer systems as described by this invention. There are several differences between cooling water systems and air washer systems, notably their uses. The main purpose of a cooling water surface is to remove heat from a surface, typically a heat exchanger, and then reject that heat to the environment, while the main purpose of an air washer is to condition the environment of the workspace. This would include both temperature and humidity control. The water of an air washer system is used to reject heat to an air conditioning machine, which is the opposite of what occurs in a cooling water system.
Another difference between the two types of systems concerns their respective methods of operation. Air washers operate in two distinct modes depending upon the season of operation. Typically during the winter, the water will evaporate and concentrate similar to a cooling water system. This occurs to increase the humidity in the work space. In the summer (higher humidity season), the water will `deconcentrate` as water is pulled from the atmosphere to reduce the humidity of the work space. The variability of water chemistry conditions that occurs due to seasonal variations is in contrast to cooling water systems that evaporate water to reject heat and are consistently at a higher cycle of concentration.
Furthermore, air washer systems are designed to scrub/clean material from the work space atmosphere, while cooling towers are designed to remove heat from a process. During this process, inadvertent contamination from the airborne contaminants occurs. Because of this design, any air washer treatments must be able to control a larger amount of airborne contaminants. For example, textile air washers will contain natural or synthetic fiber contaminants, tobacco air washers will contain tobacco dust, and electronics air washers will contain organic solvents which must be removed. Such contaminants are typically not found in cooling water systems.
The main treatment for cooling water systems is geared towards corrosion/fouling control on a heat transfer system. This is in contrast to air washer treatments being geared towards dispersancy of airborne contaminants and corrosion control of non-heat transfer surfaces. As described above, there are numerous differences between the two types of systems. In industrial water treatment, each system has a unique set of problems which can be overcome by the selection of an appropriate treatment. Since the two systems are different, a treatment suitable for one system would not also necessarily be suitable for the other. (For example, one would not use a boiler treatment program in a cooling tower where they may both be considered industrial water applications.)
Bush, U.S. Pat. No. 4,279,768 discloses a composition for removing scale built up on metallic working surfaces utilizing a synergistic blend of a chelant, polymeric conditioners, a gluconate, a triazole and sodium sulfite. Mullins, U.S. Pat. No. 4,961,878 discloses a composition of inhibiting metal corrosion in a closed aqueous cooling system which may include acrylate polymer, tolyltriazole, amine oxide and silicate.
However, neither the '878 compositions nor the '768 compositions are useful for addressing the specific problems associated with air washer systems solved by the invention described herein. The inherent differences between the two systems as described above indicate that it is not necessarily true that effective treatments for cooling water systems would be equally effective in air washer systems.
It is accordingly an object of this invention to provide to the art a novel, non-metal, non-phosphorus, high performance chemical corrosion inhibition treatment program which can be used in airwasher systems to help prevent the corrosion of the metal surfaces in contact with the water contained in such system. The corrosion inhibitors of this invention have been found to be particularly effective in preventing corrosion from occurring on the iron, mild steel, yellow metals, and galvanized steel surfaces of airwasher systems in contact with industrial cooling water.